Internal Medicine Exam Acute Kidney Injury 2 — Questions and Answers
Question 1: A 68-year-old man with chronic heart failure presents with worsening dyspnea and oliguria. Creatinine has risen from 1.2 to 2.8 mg/dL after aggressive diuresis. Urine sodium is 8 mEq/L and BUN/Cr ratio is 28. What is the most likely mechanism of AKI?
- Cardiorenal syndrome type 1 (Correct answer)
- Contrast nephropathy
- Intrinsic tubular necrosis
- Obstructive uropathy
Correct answer: Cardiorenal syndrome type 1
Cardiorenal syndrome type 1 occurs when acute cardiac decompensation causes AKI, with low urine sodium reflecting avid sodium retention due to reduced renal perfusion.
Question 2: Which of the following urine microscopy findings is most specific for acute tubular necrosis?
- Red blood cell casts
- White blood cell casts
- Muddy brown granular casts (Correct answer)
- Hyaline casts
Correct answer: Muddy brown granular casts
Muddy brown granular casts (composed of sloughed tubular epithelial cells) are the hallmark finding of acute tubular necrosis.
Question 3: A patient develops AKI after receiving vancomycin. Urinalysis shows eosinophiluria and white blood cell casts. Serum creatinine peaks at 3.1 mg/dL on day 10. What is the primary pathophysiology?
- Prerenal azotemia
- Acute interstitial nephritis (Correct answer)
- Acute tubular necrosis
- Glomerulonephritis
Correct answer: Acute interstitial nephritis
Vancomycin-induced AKI commonly causes acute interstitial nephritis, characterized by eosinophiluria, WBC casts, and a delayed onset after drug exposure.
Question 4: In the AKIN staging system, Stage 2 AKI is defined as:
- Creatinine increase ≥0.3 mg/dL or urine output <0.5 mL/kg/h for 6 hours
- Creatinine increase ≥2× baseline or urine output <0.5 mL/kg/h for 12 hours (Correct answer)
- Creatinine increase ≥3× baseline or urine output <0.3 mL/kg/h for 24 hours
- Creatinine >4 mg/dL with acute rise ≥0.5 mg/dL
Correct answer: Creatinine increase ≥2× baseline or urine output <0.5 mL/kg/h for 12 hours
AKIN Stage 2 is defined as serum creatinine increase ≥2× but <3× baseline, or urine output <0.5 mL/kg/h for ≥12 hours.
Question 5: A 55-year-old woman with lupus presents with AKI, RBC casts, proteinuria >2 g/day, and hypertension. Which diagnosis best fits this presentation?
- Prerenal AKI from volume depletion
- Acute interstitial nephritis from NSAIDs
- Lupus nephritis causing rapidly progressive glomerulonephritis (Correct answer)
- Hepatorenal syndrome
Correct answer: Lupus nephritis causing rapidly progressive glomerulonephritis
RBC casts, nephrotic-range proteinuria, and hypertension in a lupus patient indicate lupus nephritis with rapidly progressive glomerulonephritis as the cause of AKI.
Question 6: Which medication most commonly causes AKI through renal afferent arteriolar vasoconstriction leading to decreased GFR?
- ACE inhibitors
- NSAIDs (Correct answer)
- Aminoglycosides
- Calcineurin inhibitors
Correct answer: NSAIDs
NSAIDs inhibit prostaglandin synthesis, impairing afferent arteriolar dilation that normally compensates in states of reduced renal perfusion, causing prerenal AKI.
Question 7: A 72-year-old man with BPH presents with AKI and bilateral hydronephrosis on ultrasound. Bladder scan shows 800 mL of residual urine. After Foley catheter placement, urine output is 400 mL/hour. What electrolyte complication is most expected?
- Hyperkalemia and metabolic alkalosis
- Post-obstructive diuresis causing hypokalemia and hyponatremia (Correct answer)
- Hypertonic hyponatremia
- Hypercalcemia
Correct answer: Post-obstructive diuresis causing hypokalemia and hyponatremia
Post-obstructive diuresis after relief of urinary obstruction commonly causes hypokalemia and hyponatremia due to loss of electrolytes in large urine volumes.
